One area in which CT imaging systems have gained widespread acceptance is in medicine, where CT scanners are widely used by radiologists and other medical professionals in connection with the diagnosis and treatment of disease. The relatively recent adoption of multi-slice systems has further broadened the clinical application range of CT systems.
The data acquisition geometry of a conventional third generation x-ray CT system having a flat panel detector is shown in FIG. 1. FIG. 1 depicts a transaxial plane of a system, for example a central plane of a cone-beam system. An x-ray source 102 and an x-ray sensitive detector 104 are disposed on opposite sides of an examination region 106 and radially displaced from a center of rotation 114. A human patient, or other object to be examined 108 is supported in the examination region 106 by a suitable support 110. The source 102 emits radiation 112 which traverses the examination region 106 and is detected by the detector 104 as the source 102 and detector 104 rotate about a center of rotation 114.
In the illustrated full beam acquisition geometry, a central ray 116 of the x-ray beam 112 intersects the center of rotation 106 and is perpendicular to the detector transverse center 119. The detector transverse dimension 120 is such that the detector 104 detects radiation 112 which has traversed the entire transverse field of view (FOV) 118 at each projection angle. Thus, a complete angular sampling of the transverse FOV requires that data be collected over approximately 180° plus the x-ray beam 114 transverse fan angle. While illustrated in relation to a flat, panel detector, it will also be appreciated that the full beam acquisition geometry is applicable to systems in which the detector 104 is generally arcuate.
However, it is generally desirable to reduce the physical size of the detector required to achieve a given transverse FOV. For example, relatively larger detectors tend to be more complex and expensive to manufacture. Moreover, the size of the available detector arrays can be a limiting factor in the system design. These considerations become increasingly acute with the increasing popularity of multi-slice systems, and particularly as the relatively larger multi-slice detectors become a greater portion of the total system cost. In other words, in conventional 3D rotational x-ray systems, e.g. 3DRA, XperCT, CT scanners, portal imaging etc., the 3D reconstructed FOV is limited by the magnification and detector size of the detector (FOV=detector width/magnification). The magnification is the ratio between x-ray-focus-to-detector distance and x-ray-focus-to-isocenter distance. Typical values are 40 cm detector width, magnification 1.6×, thus 25 cm FOV in 3D. These systems typically scan over 180 degrees plus fan angle (˜2*arc tan(0.5*detector width/“focal point-to-detector-distance”), typically 18 degrees fan angle.
Also, half beam acquisition geometry has been proposed. See, e.g., Gregor, et al., Conebeam X-ray Computed Tomography with an Offset Detector, IEEE 2003 (2003), Wang, et al., X-ray Micro-CT with a Displaced Detector Array, Med. Phys. 29 (7), July 2002; Lin, et al., Half Field of View Reduced-Size CT Detector, PCT publication WO 00/62647, dated 26 Oct. 2000.
Consequently, there remains room for improvement. For example, it is desirable to further improve the detector utilization while maintaining a suitable image quality. It is also desirable to simplify system construction.
Aspects of the present invention address these matters, and others.